Sensors are used in various catheter-based procedures. Imaging sensors or transducers, e.g., intravascular ultrasound (IVUS) transducers, are used to help navigate the delivery of a catheter to a target site or otherwise properly orient the catheter or another instrument or device once at the target site. For example, U.S. Pat. No. 6,685,648 discloses use of an intravascular ultrasound catheter which is delivered to a remote tissue region targeted for treatment. Once at the targeted area, the catheter is properly oriented to position a needle lumen at the region. The needle is then deployed and a drug is injected into the region through the needle lumen. The catheter is configured with a single needle lumen and exit port which requires that the catheter be torqued about its longitudinal axis to rotate its distal end until the needle exit port is aligned relative to the targeted tissue region. Ultrasonic imaging is used, and in fact is required, to observe the orientation of the catheter and to ensure proper alignment of the needle with the target tissue region.
There are certain drawbacks to the catheter systems such as those disclosed in the '648 patent. Due to the unilateral configuration of the catheter, torquing of the catheter is necessary to properly align the “working” portion of the catheter, e.g., the needle exit port, with the targeted tissue region. For a catheter to be adequately torquable, certain material and physical properties are required, e.g., larger gauge, stiffer, etc., which may limit its application in smaller, more tortuous regions of the vasculature. Additionally, the catheters are required to be fitted with an orientation or imaging means such as ultrasonic transducers, which can add to the size and complexity of the system. Ultrasound in particular is limited to imaging of soft tissue, whereby pathologically calcified tissues (such as heart valves in elderly pats) or metallic structures (such as stents, guidewire) present a barrier for ultrasound penetration and imaging of tissue. Furthermore, ultrasound is complex, requires large and expensive image acquisition systems, and complex circuit designs of imaging catheters leading to increased catheter sizes. In addition, ultrasound does not provide ability to sense chemical, or electrical signals of gradients across vessel walls. Specifically, a single ultrasound transducer would produce single-dimension ultrasound signal, usually referred to as M-mode. However, chemical, physical, and biological sensors of comparable size can deliver information regarding location of a target tissue site across a membrane, e.g., a vessel wall. While less complex and size-constrained sensing means, such as chemical, electrical, thermal, biological markers placed near the distal end of a catheter may be used, these sensing methodologies may not be as accurate as ultrasound in many circumstances.
Other types of sensors, i.e., non-imaging sensors, are employed to either measure or sense various parameters in the form of signals (e.g., electrical, biochemical, thermal, biological etc) from within a vessel or body cavity. These sensors maybe configured for either temporary or permanent placement within the body. Such sensors are commonly used for the implantation of pacemakers. Implantable pacemakers are commonly used to treat hearts with abnormal rhythms in such a way that the timing and conduction of the normal cardiac electrical activity necessary for cardiac function is replaced or supplanted by artificially initiated electrical stimuli. A pacemaker consists of a pulse generator and one or more electrodes attached to the pulse generator by means of a lead or insulated wire. The electrodes may be employed to continuously monitor electrical activity of the heart as well as to transmit electrical pulses from the pulse generator to the cardiac tissue in response to the sensed signals. The output pulses cause depolarization and contraction of cardiac tissue to help in restoring cardiac function.
Pacemakers are commonly implanted in a minor surgical procedure during which the patient is mildly sedated and given a local anesthetic. Through an incision near the clavicle, the pulse generator is implanted under the skin and the leads are inserted into a vein leading to the heart. The leads are then advanced transvenously to the heart using continuous fluoroscopic guidance. The electrode is then positioned or fixed to a target site within a coronary vein within the heart, or on the surface of the heart inside the pericardial cavity.
Transvenous pacing of the left ventricle presents significant difficulties. As effective pacing requires that the electrodes be accurately placed at targeted pacing sites within the coronary veins, a catheter having imaging or sensing means is required for placing the electrodes. Due to the tortuous path to the cardiac veins, including the coronary sinus, and the small size of the distal cardiac veins, the drawbacks of current imaging catheter technologies discussed above also apply here.
Epicardially-placed electrodes can be used to pace the left ventricle. In contrast to a transvenous lead, an epicardial lead is attached to the outside of the heart. Placement of an epicardial lead requires that the surface of the heart be exposed, for example by a thoracatomy, and involves considerable operative risk in these already very sick patients. Thus, while epicardial pacing of the left ventricle is available, transvenous pacing is often more desirable.
With the limitations of current catheter technologies, there is clearly a need for an improved means and method of accessing and verifying a target site within a vessel lumen or a body cavity undergoing a catheter-based procedure, particularly a site targeted for the implantation of a device (e.g., pacing electrode, etc.) or the delivery of a material (e.g., drugs, saline, biologic compositions, etc.).